device switch 1/many: Remove d_autoq, add d_clone (where d_autoq was).
d_autoq was used to allow the device port dispatch to mix old-style synchronous
calls with new style messaging calls within a particular device. It was never
used for that purpose.
d_clone will be more fully implemented as work continues. We are going to
install d_port in the dev_t (struct specinfo) structure itself and d_clone
will be needed to allow devices to 'revector' the port on a minor-number
by minor-number basis, in particular allowing minor numbers to be directly
dispatched to distinct threads. This is something we will be needing later
on.